﻿AVICULOPECTEN. 



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2. Genus. — Aviculopecten, M'Coy. 



This genus is thus defined by Woodward : — " Shell inequivalve, sub-orbicular, 

 eared ; hinge-areas flat, with several long cartilage-furrows, slightly oblique on 

 each side of the umbones ; right valve with a deep and narrow byssal sinus 

 beneath the anterior ear ; adductor-impression large, simple, sub-central ; pedal 

 scar small and deep, beneath the umbo." There appears some difference of 

 opinion whether it should be classed with the Pectinidse or the Aviculidm; for 

 instance, Hall, Zittel, Fischer place it with the former ; S. P. Woodward and 

 Freeh with the latter. Tate, in his Appendix to Woodward's ' Manual of the 

 Mollusca,' transposes it from the latter to the former family, remarking that it 

 " does not possess the prismatic of the Aviculidse, but the peculiar corrugated 

 tubular structure of the Pectinidse (Meek). It bears the same relations to 

 existing Pectens as Pterinea does to existing Aviculas." 



Hall restricts the genus " to those forms which have the hinge-line usually 

 shorter than the transverse diameter, and both ears well-defined. Test orna- 

 mented with rays." This division seems unfortunate, as it excludes the type 

 species of the genus, Pecten granosus, Sowerby, which comes closer to Hall's new 

 genus Pterinopecten. As, however, the latter is probably, as pointed out by Freeh, 

 only to be regarded as a section or sub-genus of Aviculopecten, useful for the 

 convenient grouping of kindred shapes, rather than for markiDg any decided 

 physiological differences, it may cause less confusion simply to point out the 

 accident. 



Aviculopecten occurs from the Lower Silurian to the Permian. 



1. Aviculopecten aviformis, Whidborne. PI. X, figs. 7 — 11. 



1889. Aviculopecten aviformis, Whidborne. Geol. Mag., dec. 3, vol. vi, p. 79. 



Description. — Right valve of moderate size, very flat, more or less transverse, 

 oblique, inequilateral. Umbo minute, low, sharp, proximate, not elevated above 

 the hinge-margins, situated rather in front of the centre of the hinge-line, or 

 about one-third from the anterior extremity of the shell, and bounded on each 

 side by sharp concavities, which define the wings. Anterior wing very small, 

 acutely triangular, with sigmoid margin, flat, and well-defined. Posterior wing 

 slightly larger, acutely triangular, with concave margin, flat, and well defined. 

 Anterior margin rather broad, deeply convex. Inferior margin oblique, long, 

 moderately convex. Posterior margin straight and very oblique in the part 



